1. Field of the Invention
The present invention relates to a liquid crystal display device used as a liquid crystal display module in various kinds of electronic devices, and relates more particularly to adding a sound output function to such a liquid crystal display device. The present invention can be used in any type of electronic device having a liquid crystal display device and is particularly well suited for use in a liquid crystal display module used in portable devices such as cell phones and PDAs.
2. Description of the Related Art
Liquid crystal display (LCD) devices are typically used as the display device in cell phones, PDAs (personal digital assistants), and other portable devices. Rising demand for greater display capacity in these LCD devices has meant that the LCD screen area has also tended to grow. Furthermore, as screen size has increased so has demand for size and weight reductions in the portable devices in which the LCD devices are used. As a result, providing sufficient space for a speaker and a receiver (microphone) in a portable device also requiring a function for sound input and output has become increasingly difficult.
A transparent speaker made from a piezoelectric diaphragm including a transparent piezoelectric element and a transparent electrode, and a frame supporting the periphery of the diaphragm, has thus been proposed (see, for example, Japanese Unexamined Patent Appl. Pub. 2000-152385). A speaker function can thus be achieved without obstructing the LCD by arranging the transparent speaker over the front of the LCD panel.
A panel speaker including a diaphragm that also functions as an optical filter in the LCD device, and an exciter affixed to the back of the four edge portions of this diaphragm, has also been proposed (see, for example, Japanese Unexamined Patent Appl. Pub. 2001-189978). This panel speaker uses the same space for both the display and sound generation, and thus offers the advantage of not requiring excessive space to provide both a display and audio output.
A loudspeaker drive unit has also been achieved by driving transparent panel-shaped members disposed in front of the display surface of an LCD device, for example, with a vibration exciter disposed at the edges or peripheral portions of the panel member. (See Japanese Examined Patent Pub. 2002-533957, for example.)
A problem with these methods of the foregoing prior art is that the thickness of the device in which the display device is used increases because the speaker is arranged over the display surface. Furthermore, because the exciter (vibration source) is disposed around the edges of the LCD panel in the foregoing panel speaker, the exciter competes for space with other components similarly disposed in this peripheral area. LCD devices commonly use a light emitting diode (LED) or other light source, and installation space for this light source competes with installation space for the exciter of the foregoing panel speaker in the edge portions of the LCD panel. Using a panel speaker as described above therefore does not necessarily yield the expected space savings. As a result, the external size of the LCD device increases when a sound output function is added, and this is particularly a problem with portable devices. Furthermore, because the prior art as described above requires that a separate panel member be used as the speaker diaphragm in front of the display, the thickness of the frame (casing) in which the LCD device is housed is increased, and adding a sound output function causes a decrease in transmittance and thus degrades the quality of displayed images.